Operating Strategies for Battery Storage Systems in Low-Voltage Grids to Limit the Feed-In Power of Solar Power Systems Using Fuzzy Control

Abstract

Germany’s energy turnaround is leading to an increasing integration of photovoltaics (PVs) throughout its distribution grid. To ensure safe grid operation in times of high solar radiation, PV plants must either be throttled back to comply with the feed-in limitation or store a portion of their excess electricity in batteries. This paper presents a grid-optimized operating strategy for PV storage systems based on a Fuzzy Logic Controller that reduces peak feed-in and thus also PV curtailment losses. The Fuzzy Logic Controller uses data on PV power surplus and battery charge level as input variables. To obtain good results, the set of numerical parameters of the membership functions is enhanced by evolutionary programming. The energetic assessment shows that even small electrical storage capacities (<<5 kWh) reduce curtailment losses considerably when using the grid-optimized operating strategy. The economic assessment shows that, in 2016, investments in PV storage systems with large PV plants and small batteries have small (positive) Internal Rates of Return. The system efficiency of the battery storage has a small impact on the profitability of PV storage systems, whereas the cycle stability and the electricity purchase price have a large impact. Moreover, there is an economic benefit for plant operators to switch from the simple to the grid-optimized operating strategy. Solar forecast inaccuracies and variations in load and generation profiles have a negligible impact on the performance of the control algorithm.